At one time, automatic telephone exchanges were typically limited to providing plain ordinary telephone service, sometimes referred to as "POTS". With POTS, a telephone user may make a telephone call by dialling a telephone number which identifies the telephone set of another telephone user with whom communication is desired. The telephone user who initiates the call is referred to as a calling party, and the telephone user to whom the call is directed is referred to as a called party. A telephone call involves various elements of the telephone exchange. These elements. operate in concert to provide a communication path for the duration of the communication, be it with the called party or alternately with other means to inform the calling party that communication with the party designated by the dialled telephone number is unavailable. Depending upon prevailing conditions of the moment, each such telephone call follows a well known progression of events and is termed a call progress. A call progress is initialized when the telephone user actuates a telephone terminal apparatus. This actuation is usually referred to as going OFF HOOK. This initializing event is usually followed by some action being performed by the user. If the user is the calling party, the user indicates an identity of the called party by pressing or dialling the digits associated with the called party's telephone set, that is, the called party's telephone number. Such action will usually cause one of three typical call progresses in the telephone system, which are briefly summarized as follows:
1) The called party answers by going OFF HOOK, in response to ringing of the called party's telephone set, whereby the calling party is provided with a real time communication or conversation with the called party; PA1 2) The called party will not answer, as the called party is unresponsive to ringing or the called party is already using his telephone set, in which case the calling party has no recourse but to terminate the call progress by going ON HOOK; and PA1 3) The telephone call is intercepted by or forwarded to a voice service feature associated with the called party which answers on behalf of the called party. In this case the calling party is usually urged to leave a message for the called party, whereby the calling party may have a delayed communication transmitted to the called party.
A primary function of a voice services feature is that of is providing an opportunity for a calling party to leave a message for subsequent receipt by a called party. The first such message service was provided by a service person or a special operator who arranged to intercept telephone calls on behalf of a subscriber to the service. This personal service is relatively expensive and consequently has never become commonplace in the day to day activities of most telephone users. However, in the last decade or so, machine implementations of telephone answering and voice messaging services, which do not require the attention of a service person or a special operator, have become relatively commonplace and inexpensive to use. Telephone answering service is available by means of any of various user purchasable answering machines for use with individual telephone terminal apparatus. Alternately more sophisticated voice messaging services are available by access to a voice services feature associated with a telephone key system or a telephone exchange. Exemplary are telephone systems identified by the trademark Meridian, manufactured by Northern Telecom Limited.
If a called party is a user of a centralized voice services feature, when the called party is momentarily unavailable to answer the calling party's call, the calling party is connected with the centralized voice services feature. The voice services feature solicits a voice response from the caller on behalf of the called party. Sometime later the called party may access the voice services feature and be advised of the call by listening to the recorded voice response of the calling party. This voice message service has proven to be popular and convenient. However if the calling party has some urgent matter to discuss with the called party and the calling party is unavailable, the voice service feature is of no advantage and can be a serious impediment to achieving a real time communication. Expeditious delivery of an urgent message via a voice services feature is invariably contingent upon the called party being in the habit of frequently checking with the voice services feature for any messages.
In telephone systems available for business communications, prior to the popularity of voice services features, the availability of a busy or absent called party was enhanced by features known as "override" and "ring again". In the event that the called party was busy or failed to answer, the calling party could press a key on his telephone set to invoke the override feature or the ring again feature. In accordance with the ring again feature, when the called party subsequently went ON HOOK, the telephones of the calling party and the previously called party would be caused to ring by the telephone exchange. When both parties answered they were coupled in telephone communication, one with the other, via the telephone system. The override feature is more obtrusive than the ring again feature. In accordance with the override feature, upon receiving a busy tone the calling party is able to break into an ongoing telephone conversation. In accordance with the override feature, the telephone exchange responds to an indication from the calling party by creating a conference bridge so that the calling party becomes a full participant in the previously established telephone conversation.
The functionality of the override and ring again features has been sharply reduced by the wide spread use of voice features services. If a telephone caller finds that his call has been completed to the called party's voice message service, the caller is helpless to effect any action except to leave a voice message. If the calling party is in urgent need to communicate directly with a called party, interception by a machine can be very frustrating. In some systems the knowledgeable caller may have an option of dialling an appropriate digit to tag their message as "urgent", so that it will be identified to the called party as such, if and when the called party accesses his voice mail feature. Sometimes the calling party is given the option of either leaving a message or pressing "0" on their dial pad to speak with a secretary or an attendant. In this case, the voice services feature apparatus acts somewhat like an automated attendant by placing a second telephone call to a predetermined number. However this may only lead to greater frustration because in some instances pressing "0" only begets yet another prerecorded voice solicitation urging deposit of a voice message for the secretary. Calling party features, as provided in accordance with a calling party's class of service such as ring again and override, are simply non-functional once the calling party's call has progressed to being connected to a features server associated with the called party. As far as the call controller in the telephone exchange is concerned, the call progress has been completed through to its conversational portion. The only subsequent action to which the call controller may respond is that of either the calling party or the features server apparatus going ON HOOK. The only alternative the calling party may use in order to establish a real time conversation is to hang up, go OFF HOOK, and redial the called party's telephone number, repeatedly, until the intended telephone for which the call is destined is answered by a person. Such desperate action is time consuming for the calling party and is deleterious to the operation of the telephone exchange as frequent redialling actions have been found to be a significant consumer of processing resources in the call controller.